Pitot tubes, also known as dynamic pressure gauges, are widely used sensors in flow meter technology for determining flow velocities. A special form of a Pitot tube is the Prandtl tube, for example, which is used for speed measurement in aviation. However, dynamic pressure gauges are used in ventilation technology in measuring flow velocities, volume flows, or mass flows in ventilation ducts because they are characterized by the possibility of simple assembly and by a low pressure drop in the installed state.
A known design of such dynamic pressure gauges is illustrated in FIG. 1, for example. A probe tube 10 is inserted through an opening into the interior of a flow channel 1. Openings 11 are provided along an axis of probe tube 10 on the side of probe tube 10 facing the flow, so that a total pressure pG dependent on flow velocity vS prevails in the interior of the probe tube. The interior of probe tube 10 is connected to a first connection of a differential pressure sensor 20. A second connection of differential pressure sensor 20 is connected to another opening in the flow channel through which oncoming flow does not pass directly. The second connection of differential pressure sensor 20 is thus at a pressure level corresponding to static pressure p0 in the interior of the flow channel. Pressure difference pS=pG−p0 is known as the stagnation pressure or dynamic pressure. Flow velocity vS is calculated easily from dynamic pressure pS as follows:
                              v          s                =                                            2              ·                              p                s                                      ρ                                              (        1        )            
Symbol ρ here denotes the density of the flowing medium. The relationship above follows directly from the Bernoulli equation.
Flow velocity vS is normally not constant over the cross section of the flow channel. An average dynamic pressure pS and from this an average flow velocity vS in flow channel 10 are ascertained because probe tube 10 has multiple openings 11 along its longitudinal axis. Such a measurement of the average flow velocity is too inaccurate, however, and the particular flow profile must be included in the measurement result. In the past, this problem has been solved by adjusting and calibrating Pitot tubes individually for each possible channel cross section. This is only a minor problem with permanently installed Pitot tubes, but for mobile measurements using portable operational control meters, a probe tube adapted to each possible channel cross section would be necessary, which is not practical for mobile applications. An enormous number of different probes, namely one for each possible channel cross section, would be necessary.
Accordingly, it would be desirable to provide a measuring arrangement for determining the flow velocity in a flow channel which is suitable for performing sufficiently accurate measurements of flow velocity in tubes of any diameter.